Segisaurus (meaning "Segi canyon lizard") is a genus of small coelophysoid theropod dinosaur, that measured approximately 1 metre in length. The only known specimen was discovered in 1933 in early Jurassic strata in Tsegi Canyon, Arizona, for which it was named. Segisaurus is the only dinosaur to have ever been excavated from the area. It was later described in 1936 by the paleontologist Charles Lewis Camp. The fragmentary fossil skeleton consisted of portions of the limbs, pelvis, and vertebrae, but no cranial material was located. Segisaurus appears to have been closely related to the much more well-known Coelophysis. One distinction, however, was that Segisaurus had solid bones, while those of Coelophysis' were hollow. This even made some scientists consider if Segisaurus was even a theropod at all. Later investigations into the specimen's pelvic remains in 2005 lead scientists to believe that Segisaurus was in fact related more closely to Procompsognathus.
Description

Segisaurus lived about 180 million years ago during the Jurassic period. Segisaurus was roughly the size of a goose and was a primitive bipedal theropod. Segisaurus was roughly 1 metre long, half a metre tall and weighed about 4-7 kilograms. It was nimble and insectivorous, although it may have scavenged meat also. It was bird-like in structure, with a flexible neck, elongated neck and a stubbish body. Segisaurus was three-toed and had powerful legs that were long compared to its body length. Like its legs, Segisaurus had a long tail and long forearms. Its collar bone was not unlike a bird's, thus strengthening scientists' arguments that dinosaurs were related to avians.

Segisaurus is described from the only specimen ever found. The holotype, however, was a sub-adult, so that the full size of Segisaurus as an adult may never be known. Strangely, clavicles were found on the Segisaurus specimen, which were unknown in other dinosaurs from that era.

History of discovery

The first discovery of Segisaurus was by Max Littlesalt, a Navajo Indian who kept livestock inside Tsegi Canyon. After discovering the remains, Littlesalt pointed out the fossils to archeologists on an expedition inside the canyon. Other than the first finding of Segisaurus, no other specimens have been discovered. After its initial description by Charles Lewis Camp, the holotype went relatively ignored for the next half century. When the specimen was investigated during this period, all who viewed it commented on the presence of clavicles and the solid bone structures the dinosaur had. According to recent reports, Segisaurus is vital in understanding the evolution of early theropods.

When the specimen of Segisaurus was discovered, Camp likened it to that of a "sitting hen", due to the position the dinosaur's remains were in. Other theropods used this positions to sleep or stay sheltered during large sand storms, and indeed the Segisaurus holotype was found in a bed of sand stone, suggesting that the dinosaur had been submerged in a layer of sand and died. This is still only a hypothesis, as no nest or den materials were discovered along the Segisaurus specimen.

In September 2005, the Journal of Vertebrate Paleontology published a report which re-examined the remains of the Segisaurus holotype. The authors concluded, that although very unusual, Segisaurus was firmly a coelophysoid. They also noted that Segisaurus was probably a relative of Procompsognathus.